Method of generating the teeth of helical gear-wheels.



E. J. LEES. METHOD OF GENERATING THE TEETH OF HELICAL GEAR WHEELS. APPLICATION FILED NOV. 4. m2.

1 2%,?! Patentd Oct. 24,1916

l mum E Emeaillees UNITED STATES PATENT oEEIoE- ETBNESTJ. LEES, 0F CLEVELAND, OHIO.

METHOD OF GENERATING THE TEETH 0F HELICAL GEAR-\VHEELS.

Specification of Letters 1'. tent.

Application filed November 4, 1912. Serial No. 729,400.

so as to distinguish it from other inventions.

My invention relates to a method of generating the teeth of helical gear wheels through the agency of a helical or-hob cutter and may be carried out by certain of the mechanism shown, described, and claimed in my co-pending application upon a gear generator filed August 6th, 1909.Se-'

rial Number 511,497, and specifically by that shown in Figures3 and 11 thereof.

, To cut helical teeth-"on a gear blank with a cutter of the hob type (helically arranged generating cutter) in a machine as herein described, it is necessary that there should be a determined ratio between the rotation of the cutter, the rotation of the gear blank, and thefeedof the work or blank across the cutter in a line parallel with the axis of the blank.

Fig. 1 is a top plan of a gear generator suitable for carrying out my inventive method. Fig. 2 is an end view ofthe same,

showing both the rotation and the feed change gears. Fig. 3 i s' a diagrammatic view of a helical gear used to describe and formulate the cutting of a helical gear by parts of n n is the feed of the Work across the cutter to every revolution of the blank, n is the angle of the teeth With theaxis W, of the gear N, a is the intersection of one edge of the tooth with the edge of the gear blank, and n is the intersection of n with the edge of the tooth.

Before describing this method, an exslowed down instead of increased.

ample of a gear taken in connection with diagram of Fig. 3 will make it clear. It is understood that a single thread cutter is being used, the gear to be of the following dimensions: twentv teeth: one inch circular pitch; 40 angle of teeth with axis.

Patented. Oct. 24, 19m.

Referring'again to Fig. 3, it-is very evident-that if the cutter should start to cut at a by the time it had reached the point 02. the blank N would have to revolve more than one revolution, providing of course we are cutting a right hand gear with a right hand cutter. It is equally obvious that where it is desired to cut a left hand helical gear with a left hand cutter, the formula usedis the same, the machine rotate the blanks in the oppositedirection, while to cut a right hand gear with a left hand cutter the rotation of the blank is.

An example of this, assuming we are to cut a twenty tooth gear with a one inch circular pitch and a 45 angle right hand. is accon1- plished by gearing up the machine to cut twenty and one-eighth (20%) teeth per rotation and atthe same time gearing up the machine to feed one-eighth per revolution.

It is very evident that nineteen and seveneighths (19%) teeth are less than twenty (20) teeth, and that in a machine of this type to out spur gears the cutter and blank revolve at a ratio corresponding to the number of teeth to be cut. It is also evident then of course being geared up in such'event to that a gear with nineteen and sevcn-eighths (19%) teeth will rotate faster than a gear with'twenty (20) teeth. Therefore, if we gear upthe machine tofcut nineteen and severe eighths (19%) teeth, the blank will be rotated one-eighth of the circular pitch of gear with twenty" (20) teeth oneinch circular pitch 45 angle. It is very evident that on any other angle outside of 45 the ratlo between a and we will not be one to one, as in this case, therefore it isnecessary to follow a fixed formula to determinethero tation and thejfeed. The following data must be known: number of teeth in gear to be cut; normal pitch; circularpitch 11 angle of teeth with axis n tangent of angle of teeth; co-tangent of angle of teeth; cosineof angle of teeth. This information is used in conjunction with formulae as fol-'- lows ' n or approximate fractional tangent of n X approximate feed P of tooth- The rotation should" be geared up to the number of teeth to be cut minusithe nearest available even fractional part to n which can be expressed as a mixed number.

Having now decided the rotation, the formula for thefeed isi X cotangent of angle= approximate feed or 12'.

Some'fig'ure with which it is easy to computeisgene'rally assumed for the factor I? which latter approximately determines the feed n. This formula does not differ from the example already given, since it was the circumstance of the example given having an angleof 45 which made it possible to determine the ratio of n to nfiinentally, hence following the formula, the, cotangent of L459Qbeing one, the result is the same.

The operation of this machine is' as follows: The, cone pulley G supplies'the ro tation or-power to the-machine. The shaft G is driven by cone G and in-turn drives shaft B which in turn drives shaft -B* which in turn drives B, which is the cutter spindle driving the cutter which generates the teeth in the gear blank, The

shaft G meanwhile drives the gear G i 'gear J through the medium of .a suitable clutch drives a shaft on which the gear 6 is fastened, and this gear 6 then drives gear 7, which in-turn drlves gear'8, which again "in turn-drives gear 9, which drives the screw O", which feeds the work slide C imparting the feed motion to the main spindle C and to-the gear blanks to be cut parallel to the axis of the gears.

The application of the foregoing formula to the machine may be as follows: To set up the machine to cut a helical gear of the dimensions called for in the example already given namelyz'twenty (20) teeth; one inch circular pitch; 45 angle of teeth with axis. Arrange gears 1, 2, 3, 4, 5, so that while the cutter moves through twenty revolutions, the

- gear blanks will have gone one revolution "plus one-ei hth (-2,) of the circular pitch; .or inother words gear up the rotation to cut nineteen and seven-eighths (19%) teeth As for the feed, arrange gears 6, 7, 8 and 9 a so that while the work spindle goes one revolution the work slide C will travel one eighth (l of an inch parallel to} the axis of the gears to be out.

It will be notlced that while the normal I pitch and cosine of theqangle are both required to. be known, no mention has been made'of their function which is as follows:

A helical gear is often specified by normal :circular pitch and not circular pitch. In this case the circular, pitch is found in the following manner: Divide normal circular pitch by cosine of angle and the result will equal circular pitch or W which isa quantity that" must be known.

Having now fully described my invention,

what Iclaim and desire to secure by Letters Patent is v j A method of generating the teethfof'heli cal gear wheels having difierent numbers of teeth, consisting in rotating a gear blank and helical cutter with relative speeds through a single, continuous and unvarying motion from a driver to said various gear blanks and cutter respectively, said relative rotations being determined by the ratio of the number of teeth of each gear to be cut to the number of threads in the cutter plus -or minus a proportionate constant increment; and imparting a fixed proportionate feeding motion, according to the number of teeth in the. blank which is being operated upon, substantially parallel to the axis of Y and relative-to the rotation of the particular gear blank whereby to maintain a constantangle in producing helical teeth on said blanks that have a directrix coinciding with the axes of the gear blanks. Signed-by me, this first day of November,

1912. I I n ERNEST J. LEES.

Attested by a LYNN E. MUELLER,

H. F. LEIoK. 

